Look at the areas with way lots more people and a longer history of human habitation than North and South america. What's happening to wildlife in Africa? They coexisting well with the people? Or India and China?

The earth has a fixed amount of resources. We are not creating more land, water, minerals, etc. We do recycle, but no more is made.

We can, to some point, conserve our way out of short term problems. But not in the long term.

Say a river, in its pristine state, supported 1000 people with their annual need of salmon for food. You now have 2,000 trying to live of that run. Or 3 or 4 or 10,000. At some point, the run can't sustain itself. Before it hits that point, the other resources that ate salmon or depended on the spawners for nutrients have to decline because humans have taken "their share". Same argument holds for water and any other resource.

People seem to think that our existence is somehow outside of the rules that govern ecosystems. We're not.